3 New Ways Detroit Could Convert Electricity Into MPG

Oct 1, 2009

Cars may be more and more efficient these days, but they still waste more than 60 percent of the energy they consume, mostly due to heat lost through the exhaust system or radiator. Saving even a small fraction of that energy—as little as seven or eight percent—by using thermoelectric generators that convert heat into electricity could save 1.5 billion gallons of diesel a year in heavy trucks alone, according to Clemson University physicist Terry Tritt.

"Thermoelectric generators are currently used in NASA's deep-space probes to convert the heat of radioactive elements to electrical energy," Tritt told a Department of Energy (DoE) conference in Dallas last week. "One of the more promising 'down-to-earth' applications lies in waste-heat recovery in cars."

By relying on a material class that develops voltage when there's a temperature difference across them, thermoelectric devices have helped NASA power spacecraft for some 30 years. But the last decade has seen a wave of new research in the field, drawing interest from programs such as the DoE's Freedom Car initiative. Though they would still have to enhance the efficiency of power recovered from thermoelectric generators, researchers are considering these three main options to thermo-fuel your car ... someday:

1. Power the Electrical Systems
Thanks to the increased use of electrical systems such as stability control, telematics, collision avoidance systems, navigation systems, steer-by-wire and electronic braking, the average electrical demand in a midsize car rose from less than 1 kw in 2000 to about 3.5 kw in 2005, according to GM researcher Jihui Yang. This load is a serious drain on fuel efficiency.

2. Propulsion
Using the hybrid electric drive in cars such as the Toyota Prius, electrical power can be channeled directly back into pushing the car forward. It's the most direct way to reduce fuel consumption—assuming you have some electricity left after powering the electrical systems listed above.

3. Cooling
A thermoelectric cooling system could replace the air conditioner, saving a billion barrels of oil day if it was adopted by 90 percent of vehicles by 2020, according to DOE projections. Thermoelectric air conditioning has been tested on the USS Dolphin submarine, since it's a solid-state technology with no moving parts that can operate in "silent mode."

There are other thermoelectric consumer devices on the market, like the Citizen Eco-Drive Thermo watch, which converts the temperature difference between your body and the surrounding air into electrical energy. Coleman and Igloo also offer thermoelectric coolers, and some luxury cars have climate-controlled seats that are thermoelectrically powered.

For automotive applications, the best current prototypes generate about 0.3 kw. The Freedom Car roadmap calls for a 1-kwsystem, improving fuel efficiency by 10 percent, and ready for rollout between 2011 and 2014. The challenge, Tritt says, is developing advanced materials in which the thermoelectric effect is two or three times stronger than in current materials—and that number is still up for debate. Still, such a level of performance has already been achieved in a range of exotic nano-materials, but they are too small and too expensive to power a car. However, combining the nano-materials with current thermoelectric materials—as a thin coating, for instance—has shown promise in experiments, scientists say. —Alex Hutchinson

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